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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
/**
* \file AtomicCounter.h
*/
#ifndef qpid_asyncStore_jrnl2_AtomicCounter_h_
#define qpid_asyncStore_jrnl2_AtomicCounter_h_
#include "ScopedLock.h"
namespace qpid {
namespace asyncStore {
namespace jrnl2 {
/**
* \brief Template integral atomic counter class which provides a next() operation to increment then return the
* updated count of integral type T. This operation is performed under a thread lock.
*/
template <class T> class AtomicCounter
{
public:
/**
* \brief Constructor with an option to set an inital value for the counter.
*/
AtomicCounter(T initialValue = T(0)) :
m_cnt(initialValue)
{}
/**
* \brief Destructor
*/
virtual ~AtomicCounter()
{}
/**
* \brief Increment, then return new value of the internal counter. This is thread-safe and takes a lock
* in order to perform the increment.
*
* \note This is a non-zero counter. By default, the counter starts with the value 0, and consequently the
* first call to next() will return 1. Upon overflow, the counter will be incremented twice so as to avoid
* returning the value 0.
*/
virtual T next()
{
// --- START OF CRITICAL SECTION ---
ScopedLock l(m_mutex);
while (!++m_cnt) ; // Cannot return 0x0 if m_cnt should overflow
return m_cnt;
} // --- END OF CRITICAL SECTION ---
protected:
T m_cnt; ///< Internal count value
ScopedMutex m_mutex; ///< Internal lock used to increment the counter
};
}}} // namespace qpid::asyncStore::jrnl2
#endif // qpid_asyncStore_jrnl2_AtomicCounter_h_
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